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Update

... Continued discussion of rewiring a single bushing pole pig:

Well the operation appears to have been a success and the pig is
recovering nicely...

To get to the core of the pig I had to remove a grounding strap
connecting the lid to the can, then loosen and remove the com-
pression ring that clamps the lid down. With the compression ring
removed I unsealed the lid with some gentle persuasion from a
flat bladed screwdriver. After loosening the lid, I lifted it
gently and slid it back. The lid from a pig cannot be completely
removed unless you get under the oil and disconnect the high-
voltage lead(s) from the base of the HV bushing. With a single
bushing pig (like this one was) it is usually sufficient to
simply pivot the lid around on the HV lead wire and then lean the
lid to the side.

With the lid moved out of the way, I used a powerful flashlight
to examine the grounded end of the HV winding beneath the oil. 
It was pretty clear that the core is a standard design, meaning
that the HV winding was designed to be used in either one or two
bushing applications. On to rewiring!

I got some RG-213 coax with the solid polyethylene jacketed core
and cut off about a meter. I slipped the core of the coax out of
the sheath, bared one end, then soldered on a ring terminal. Eye-
balling the ring terminals on both ends of the HV winding under
the oil I figured that 1/4 inch diam. fasteners would be suitable
for making a ring terminal splice/connection. Next I laid out a
selection of some 1/4 inch brass screws, flat washers, and nuts;
all cleaned and ready to go. Then I cleaned up a set of socket
extensions and sockets, and had a stack of clean linen towels on
standby.

My brother assisted in the actual operation after I washed and
thoroughly dried my hands. Using a 3/8 inch socket on a long
extension I was able to loosen the bolt that fastened the
grounded end of the HV winding to the core. Reaching down into
the oil I removed the fastener and handed it out to my brother
who in turn handed me the HV rated wire. Working carefully under
the oil, and using thoroughly cleaned tools, I was able to
connect what had been the grounded end of the HV winding to my
length of poly jacketed coax core using the 1/4 inch brass
hardware I had prepared. Snugging the hardware down firmly
completed this portion of the task and I went on to wipe/wash 
off the oil.

The voltage rating on the plate of a pig can be rather mis-
leading. The HV winding on the plate of this pig is marked (and I
quote):  
                    HV 12470GRDY/7200
The important voltage figure is stamped after the slash "/" on
these plates, so I knew the newly rewired unit was going to have
a 7200 volt output from the high-voltage winding. Since I was
taking single steps at a time, I went on to stabilize the new HV
lead coming out of the oil before undergoing any further testing
or rewiring. 

I positioned and braced the lid so that I could drill a hole
through the flat section where the second HV bushing would have
been mounted. A 19/64 inch drill bit allowed perfect clearance
for the coax core. Next there was an insulation question
concerning my bare splice flopping around in the can. After some
thought I rolled up some 60 mil polyethylene into a tube four
inches long and two layers thick. I held the tube together with
some nylon wire ties and slid it down under the oil on the new
lead wire. Using a long screwdriver I slid the poly tube over my
splice and all the way down to the winding. This insulator allows
some movement but prevents the lead wire or splice connection
from coming into contact with any other conductors in the can.
Having prevented this potential problem, I fed the new HV lead
through the hole in the can and bolted the lid back in place.

Most single bushing pigs have bolt hole fittings on the side of
the can for a bolt-on ground bushing. Using these threaded holes
on the side of the can, I bolted on a heavy commercial insulator
that is equipped with a stainless steel terminal rated at 10KV in
outdoor applications. After cutting and baring the end on my new
HV lead wire, I soldered on a large ring terminal and fastened it
to the top of the "add-on" insulated bushing. Next I proceeded to
determine the exact turns ratio of the pig and the true output
voltage with 240-280 inputs.

Using a VOM with a high voltage setting I was able to determine a
turns ratio of 30 between the primary/secondary, which matched
perfectly to the plate. I need a 14,400 volt two bushing supply,
so some more modifications would be required, however I decided
to stop and test things out under load. Running lead wires to my
rails I fired a Jacob's Ladder at 7200 volts and ascertained that
things were looking good.

At this point I was determined to stop and fire a coil of some
type, so I went into a flurry of activity and roughed out a
simple RF ground right in the corner of the new lab. The
foundation drain sump was holed and I drove in a four foot length
of 3/4" conduit left over from the 240 volt 100 amp wiring last
weekend. I filled the sump with water and measured the time
required for it to empty... Too fast. A quick trip to the store
and I returned with 40 lbs of water softener salt and large bag
of clay cat box filler. Mixing salt and cat box filler in the
sump, then filling with water and mixing some more, formed a
slurry that slowed the drainage down to the point where the salt
water level dropped about an inch every ten minutes or so. I fed
10 foot lengths of stainless steel strapping and soft copper
tubing into the drain pipe feeds from the foundation. Connected
to this salty sump, I unrolled some aluminum flashing across the
floor and taped it down flat to the concrete with duct tape. 

I hauled out an old 8" diam. secondary coil wound on PVC pipe, my
15 turn flat pancake primary, 20" commercial spun aluminum
toroid, .025 uF Condenser Products cap from the last group
purchase, and my small fixed speed rotary gap. Bringing in HV
power from the newly re-wired pig, I got the rotary gap to fire
by closing the electrodes to the closest possible point without
hitting. After a few tap adjustments to get the tune squared away
I was breaking out with solid 4 foot sparks, despite the fact
that the arc welder was on the lowest power setting and no
resistive ballast was used in parallel. Heck, the ammeter on my
power cabinet was just barely moving, if it moved at all. There
was virtually no voltage drop. With the variacs dialed all the
way up I was probably sending all of 8400 volts to the coil. 

I can say the heavier transformer was very smooth. Lighter 5 and
even 10 KVA pigs seem to be "led around" at times by even a
medium sized coil. When using strictly inductive ballast on a
medium sized coil I frequently encounter some inductive surging
through the control circuits. You can sometimes hear and see some
oscillation at the spark gap; as the sound and light peaks and
ebbs at the frequency of the inductive delay, usually a sig-
nificant fraction of a second on a medium-large coil. This coil
was pulling on the 25 kVA pig, but the pig was not budging. 

Rock solid and smooth, there was no surging at all after the
initial powerup. This was despite the fact that I was using a
fixed speed rotary gap with no resistive ballast, or, just the
situation where I would have expected a problem. This was one
case where the pig clearly had the better of the coil. I have
heard some pig coilers state that the heavier pigs are not as
efficient, that they required too much energy to energize the
core, and that the lighter pigs are better for coiling. My few
minutes experience in handling the heavier 25 kVA pig leads me to
seriously doubt this old wisdom. I really felt a difference. I
really liked the heavier core, even with the arc welder cranked
all the way down.

BTW, this was still enough to raise Cain. All the hard wired
smoke detectors (four of them) went off upstairs and my wife came
running down to tell me that "lightning bolts" were shooting
across the upstairs hall. The local EMFs from coiling are enough
to trip many fire detectors, and mine have every appearance of
being especially sensitive (they seem to go off every time I boil
water on the stove or a plane flys low overhead). These smoke
detectors will have to be taken off-line before I power up again.
The "lightning bolts" across the hall were just that. There was a
small wire hanging from the sheetrock firewall above the garage.
This is the switch wire for the optional overhead door unit which
will never be installed in my garage. I had neglected to tie it
up and throw an RF shield around it, and so it had been struck
every few seconds. The coil was powerful enough that sparks were
leaping off the carpet and flooring nails every time the wire was
struck. That is a simple shielding issue, but I still have some
work to do before things get to the point where I can up the
power levels.

Back to the pig: Today I popped the lid off again and rewired my
LV windings. I placed both windings in parallel, which in many
ways was even harder than rewiring the HV winding. One end of
each low voltage winding was a very heavy and thick aluminum
strap. The straps had to be bent, rerouted, and bent again in
order to place the LV windings in parallel. This was actually
pretty tough, being that everything was oily, I did not want to
put a bunch of dirty tools in there, and my clearance was reduced
with the added HV terminal restricting the lid position. I ended
up using a wooden drift pin and a hammer to reposition the heavy
straps, and a pair channel-lock pliers to twist and pull the
straps up onto the terminal pins. I had one section where the two
straps crossed in direct contact, and I did not trust the paper
wrap as it had been scraped around, so I beefed up the insulation
with a strip of 60 mil poly that I friction fitted where the two
heavy straps crossed. Once bolted into place, neither the straps
nor the poly moved.

All said for an done I rechecked the turns ratio to make sure the
pig was rewired correctly: two HV bushings, 14400 volts output
with 240v inputs. Putting on the VOM I was able to determine the
new primary/secondary turns ratio at 1:60 with both LV
"primaries" in parallel. So far, so good. It was getting late so
I decided to high-pot test again tomorrow after I do some RF
ground shielding around the coil.

Richard Quick


... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12